1. Field of the Invention
The present invention relates to a power supply transformer for a telephone to be incorporated in an AC adapter as a power supply for the telephone.
2. Description of the Prior Art
FIG. 3 is a block diagram showing a configuration of a power supply system related to a telephone set using a power supply transformer for a telephone according to a conventional example. In the drawings, an AC adapter 21, is configured by a power supply transformer 22 and a rectifying portion 23, etc., and converts a commercial power supply (AC120V60 Hz) which is an input into a predetermined DC voltage to be outputted.
In a charging stand 25, there are installed a stabilizing power supply 27, which stabilizes a DC output from the AC adapter 21 to implement outputting to a charging terminals 25a, and a modem 16 of the telephone set, which receives a power supply from this stabilizing power supply 27, or the like. In an extension phone of the telephone set, etc., which is displaced on the charging stand 25, a built-in battery is charged with charging currents from the charging terminals 25a. 
The modem 16 implements modulation-demodulation between a telephone line 10 and the telephone set for DC voltages of 75 to 200 V via a line transformer 28.
Thus, insulation (for the telephone set) is implemented by using separate transformers respectively for a commercial power supply line (AC 120 V in 60 Hz) and the telephone line 10.
However, safety standards on electric insulation were intensified so as to give rise to a necessity that the sufficient insulation distance between a primary side and a secondary side should be also secured as to the line transformer 28 inserted between the telephone line 10 and the modem 16.
Object of the Invention
Contemplating on such points, the present invention is accomplished, and the purpose of the present invention is to provide a new power supply transformer for telephone in order to realize good cost performance while complying with the standards of the power supply system related to the telephone set caused by strengthening the safety standards.
It is also one of measures for the safety standards to improve the line transformer 28 inserted between the telephone line 10 and the modem 16 to secure insulation distance on insulation between a primary side and a secondary side. However, according to the present application, the power supply transformer for telephone is configured by respectively independent two secondary side circuits, and one is used for charging as in a conventional one and the other is used for power supply to the modem 16. This enables the telephone line 10 to directly connect with the modem 16 by omitting the line transformer 28.